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Rewrite the FSM. Instead of relying on a fixed-size shared memory segment, the

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free space information is stored in a dedicated FSM relation fork, with each
relation (except for hash indexes; they don't use FSM).

This eliminates the max_fsm_relations and max_fsm_pages GUC options; remove any
trace of them from the backend, initdb, and documentation.

Rewrite contrib/pg_freespacemap to match the new FSM implementation. Also
introduce a new variant of the get_raw_page(regclass, int4, int4) function in
contrib/pageinspect that let's you to return pages from any relation fork, and
a new fsm_page_contents() function to inspect the new FSM pages.
This commit is contained in:
Heikki Linnakangas
2008-09-30 10:52:14 +00:00
parent 2dbc0ca937
commit 15c121b3ed
53 changed files with 1844 additions and 2720 deletions
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352
src/backend/storage/freespace/fsmpage.c Normal file
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/*-------------------------------------------------------------------------
*
* fsmpage.c
* routines to search and manipulate one FSM page.
*
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/freespace/fsmpage.c,v 1.1 2008/09/30 10:52:13 heikki Exp $
*
* NOTES:
*
* The public functions in this file form an API that hides the internal
* structure of a FSM page. This allows freespace.c to treat each FSM page
* as a black box with SlotsPerPage "slots". fsm_set_avail() and
* fsm_get_avail() let's you get/set the value of a slot, and
* fsm_search_avail() let's you search for a slot with value >= X.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "storage/bufmgr.h"
#include "storage/fsm_internals.h"
/* macros to navigate the tree within a page. */
#define leftchild(x) (2 * (x) + 1)
#define rightchild(x) (2 * (x) + 2)
#define parentof(x) (((x) - 1) / 2)
/* returns right sibling of x, wrapping around within the level */
static int
rightsibling(int x)
{
/*
* Move right. This might wrap around, stepping to the leftmost node at
* the next level.
*/
x++;
/*
* Check if we stepped to the leftmost node at next level, and correct
* if so. The leftmost nodes at each level are of form x = 2^level - 1, so
* check if (x + 1) is a power of two.
*/
if (((x + 1) & x) == 0)
x = parentof(x);
return x;
}
/*
* Sets the value of a slot on page. Returns true if the page was
* modified.
*
* The caller must hold an exclusive lock on the page.
*/
bool
fsm_set_avail(Page page, int slot, uint8 value)
{
int nodeno = NonLeafNodesPerPage + slot;
FSMPage fsmpage = (FSMPage) PageGetContents(page);
uint8 oldvalue;
Assert(slot < LeafNodesPerPage);
oldvalue = fsmpage->fp_nodes[nodeno];
/* If the value hasn't changed, we don't need to do anything */
if (oldvalue == value && value <= fsmpage->fp_nodes[0])
return false;
fsmpage->fp_nodes[nodeno] = value;
/*
* Propagate up, until we hit the root or a node that doesn't
* need to be updated.
*/
do
{
uint8 newvalue = 0;
int lchild;
int rchild;
nodeno = parentof(nodeno);
lchild = leftchild(nodeno);
rchild = lchild + 1;
newvalue = fsmpage->fp_nodes[lchild];
if (rchild < NodesPerPage)
newvalue = Max(newvalue,
fsmpage->fp_nodes[rchild]);
oldvalue = fsmpage->fp_nodes[nodeno];
if (oldvalue == newvalue)
break;
fsmpage->fp_nodes[nodeno] = newvalue;
} while (nodeno > 0);
/*
* sanity check: if the new value value is higher than the value
* at the top, the tree is corrupt.
*/
if (value > fsmpage->fp_nodes[0])
fsm_rebuild_page(page);
return true;
}
/*
* Returns the value of given slot on page.
*
* Since this is just a read-only access of a single byte, the page doesn't
* need to be locked.
*/
uint8
fsm_get_avail(Page page, int slot)
{
FSMPage fsmpage = (FSMPage) PageGetContents(page);
return fsmpage->fp_nodes[NonLeafNodesPerPage + slot];
}
/*
* Returns the value at the root of a page.
* Since this is just a read-only access of a single byte, the page doesn't
* need to be locked.
*/
uint8
fsm_get_max_avail(Page page)
{
FSMPage fsmpage = (FSMPage) PageGetContents(page);
return fsmpage->fp_nodes[0];
}
/*
* Searches for a slot with min. category. Returns slot number, or -1 if
* none found.
*
* The caller must hold at least a shared lock on the page, and this
* function can unlock and lock the page again in exclusive mode if it
* needs to be updated. exclusive_lock_held should be set to true if the
* caller is already holding an exclusive lock, to avoid extra work.
*
* If advancenext is false, fp_next_slot is set to point to the returned
* slot, and if it's true, to the slot next to the returned slot.
*/
int
fsm_search_avail(Buffer buf, uint8 minvalue, bool advancenext,
bool exclusive_lock_held)
{
Page page = BufferGetPage(buf);
FSMPage fsmpage = (FSMPage) PageGetContents(page);
int nodeno;
int target;
uint16 slot;
restart:
/*
* Check the root first, and exit quickly if there's no page with
* enough free space
*/
if (fsmpage->fp_nodes[0] < minvalue)
return -1;
/* fp_next_slot is just a hint, so check that it's sane */
target = fsmpage->fp_next_slot;
if (target < 0 || target >= LeafNodesPerPage)
target = 0;
target += NonLeafNodesPerPage;
/*
* Start the search from the target slot. At every step, move one
* node to the right, and climb up to the parent. Stop when we reach a
* node with enough free space. (note that moving to the right only
* makes a difference if we're on the right child of the parent)
*
* The idea is to graduall expand our "search triangle", that is, all
* nodes covered by the current node. In the beginning, just the target
* node is included, and more nodes to the right of the target node,
* taking wrap-around into account, is included at each step. Nodes are
* added to the search triangle in left-to-right order, starting from
* the target node. This ensures that we'll find the first suitable node
* to the right of the target node, and not some other node with enough
* free space.
*
* For example, consider this tree:
*
* 7
* 7 6
* 5 7 6 5
* 4 5 5 7 2 6 5 2
* T
*
* Imagine that target node is the node indicated by the letter T, and
* we're searching for a node with value of 6 or higher. The search
* begins at T. At first iteration, we move to the right, and to the
* parent, arriving the rightmost 5. At the 2nd iteration, we move to the
* right, wrapping around, and climb up, arriving at the 7 at the 2nd
* level. 7 satisfies our search, so we descend down to the bottom,
* following the path of sevens.
*/
nodeno = target;
while (nodeno > 0)
{
if (fsmpage->fp_nodes[nodeno] >= minvalue)
break;
/*
* Move to the right, wrapping around at the level if necessary, and
* climb up.
*/
nodeno = parentof(rightsibling(nodeno));
}
/*
* We're now at a node with enough free space, somewhere in the middle of
* the tree. Descend to the bottom, following a path with enough free
* space, preferring to move left if there's a choice.
*/
while (nodeno < NonLeafNodesPerPage)
{
int leftnodeno = leftchild(nodeno);
int rightnodeno = leftnodeno + 1;
bool leftok = (leftnodeno < NodesPerPage) &&
(fsmpage->fp_nodes[leftnodeno] >= minvalue);
bool rightok = (rightnodeno < NodesPerPage) &&
(fsmpage->fp_nodes[rightnodeno] >= minvalue);
if (leftok)
nodeno = leftnodeno;
else if (rightok)
nodeno = rightnodeno;
else
{
/*
* Oops. The parent node promised that either left or right
* child has enough space, but neither actually did. This can
* happen in case of a "torn page", IOW if we crashed earlier
* while writing the page to disk, and only part of the page
* made it to disk.
*
* Fix the corruption and restart.
*/
RelFileNode rnode;
ForkNumber forknum;
BlockNumber blknum;
BufferGetTag(buf, &rnode, &forknum, &blknum);
elog(DEBUG1, "fixing corrupt FSM block %u, relation %u/%u/%u",
blknum, rnode.spcNode, rnode.dbNode, rnode.relNode);
/* make sure we hold an exclusive lock */
if (!exclusive_lock_held)
{
LockBuffer(buf, BUFFER_LOCK_UNLOCK);
LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
exclusive_lock_held = true;
}
fsm_rebuild_page(page);
MarkBufferDirty(buf);
goto restart;
}
}
/* We're now at the bottom level, at a node with enough space. */
slot = nodeno - NonLeafNodesPerPage;
/*
* Update the next slot pointer. Note that we do this even if we're only
* holding a shared lock, on the grounds that it's better to use a shared
* lock and get a garbled next pointer every now and then, than take the
* concurrency hit of an exlusive lock.
*
* Wrap-around is handled at the beginning of this function.
*/
fsmpage->fp_next_slot = slot + (advancenext ? 1 : 0);
return slot;
}
/*
* Sets the available space to zero for all slots numbered >= nslots.
* Returns true if the page was modified.
*/
bool
fsm_truncate_avail(Page page, int nslots)
{
FSMPage fsmpage = (FSMPage) PageGetContents(page);
uint8 *ptr;
bool changed = false;
Assert(nslots >= 0 && nslots < LeafNodesPerPage);
/* Clear all truncated leaf nodes */
ptr = &fsmpage->fp_nodes[NonLeafNodesPerPage + nslots];
for (; ptr < &fsmpage->fp_nodes[NodesPerPage]; ptr++)
{
if (*ptr != 0)
changed = true;
*ptr = 0;
}
/* Fix upper nodes. */
if (changed)
fsm_rebuild_page(page);
return changed;
}
/*
* Reconstructs the upper levels of a page. Returns true if the page
* was modified.
*/
bool
fsm_rebuild_page(Page page)
{
FSMPage fsmpage = (FSMPage) PageGetContents(page);
bool changed = false;
int nodeno;
/*
* Start from the lowest non-leaflevel, at last node, working our way
* backwards, through all non-leaf nodes at all levels, up to the root.
*/
for (nodeno = NonLeafNodesPerPage - 1; nodeno >= 0; nodeno--)
{
int lchild = leftchild(nodeno);
int rchild = lchild + 1;
uint8 newvalue = 0;
if (lchild < NodesPerPage)
newvalue = fsmpage->fp_nodes[lchild];
if (rchild < NodesPerPage)
newvalue = Max(newvalue,
fsmpage->fp_nodes[rchild]);
if (fsmpage->fp_nodes[nodeno] != newvalue)
{
fsmpage->fp_nodes[nodeno] = newvalue;
changed = true;
}
}
return changed;
}